1. Field of the Invention
The present invention relates to a sheet conveying apparatus, an image reading apparatus including the sheet conveying apparatus, such as a copier, a facsimile, a printer, a printing machine, an ink-jet recording apparatus, and a scanner, and an image forming apparatus, such as a multifunction product formed in combination of at least two of the above functions.
2. Description of the Related Art
Conventionally, in image forming apparatuses, such as a copier including a plain paper copier (PPC), a facsimile, a printer, a printing machine, and an ink-jet recording apparatus, to achieve downsizing of the entire apparatus, its conveying unit also tends to be downsized. Such a conveying unit is for conveying and supplying, from a sheet accommodating unit or a sheet stacking unit to an image forming unit body, a medium subjected to image formation or a sheet-like recording medium (hereinafter “sheet”) on which an image is formed. The sheet accommodating unit that accommodates sheets is exemplarily explained below.
Also, of these image forming apparatuses, many models generally support various sheet sizes (hereinafter, “paper sizes”) or sheet types (hereinafter, “paper types”). In these models of image forming apparatuses, for example, sheets (hereinafter, “papers”) of several paper sizes and paper types are accommodated in advance in sheet accommodating units. Then, a paper is supplied from a sheet accommodating unit selected by the user as appropriate, or a paper automatically selected by the image forming apparatus is supplied. With such a configuration, the sheet accommodating units occupy and consume a larger space in the image forming apparatus, and therefore demands for downsizing each conveying unit are increased.
For this reason, a conveying path formed between the sheet accommodating unit and the image forming unit body in the image forming apparatus is significantly changed in its conveying direction depending on the positional relation between these units to reduce the occupied space of the conveying path itself. To successively and smoothly change the conveying direction, a curvature portion in a curved shape is provided on the conveying path, and a radius of curvature of the curvature portion is set small so that a standard-sized recording paper as a sheet for normal use in the image forming apparatus can be conveyed.
An example in the conventional technology of a sheet conveying apparatus in the image forming apparatus as mentioned above is shown in FIG. 16. That is, as shown in the drawing, an image forming unit body not shown includes stages on a lower side, each of which having disposed therein a sheet accommodating unit 101 including a paper feeding tray 109 having accommodated therein a predetermined number of stacked papers S of a predetermined paper size and paper type. Between the paper feeding tray 109 and the image forming unit body, a paper conveying apparatus (sheet conveying apparatus) 102 is provided that draws one paper S0 in an approximately horizontal direction from the selected paper feeding tray 109 and feeds it upward toward the image forming unit body. The paper conveying apparatus 102 has fixed thereto curved guide members 103 and 104 that guide the paper S0 by successively changing a sheet proceeding direction from an approximately horizontal direction to an approximately upward direction (which is also an approximately vertically-upward direction). These fixed curved guide members 103 and 104 form the curvature portion mentioned above, and also a paper conveying path (sheet conveying path) A0 is formed. In the drawing, B denotes a paper conveying path for upward-feeding of a paper S of another paper size or paper type accommodated in a paper feeding tray at a lower stage.
Here, the paper conveying apparatus 102 shown in FIG. 16 is an equivalent device specifically represented for comparison between an example of the conventional technology disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-338923, FIGS. 6A to 6C and 7, and a paper conveying apparatus (sheet conveying apparatus) according to embodiments of the present invention, which will be explained further below.
The curved guide member 103 has formed thereon a fixed guide surface 103A that curves in an approximately convex shape for guiding the paper S. The curved guide member 104 is externally provided with reference to the paper conveying path A0 of the curvature portion to internally face the curved guide member 103. This external curved guide member 104 has formed thereon a fixed guide surface 104A that curves in an approximately concave shape to face the fixed guide surface 103A. At the end of a downstream in a paper conveying direction in the fixed guide surface 104A, a flexible sheet feeler 104a that is made of Mylar or the like and is elastically deformable is provided to extend to a nip portion of paired rollers 106, which will be explained further below.
Reference numeral 105 denotes paired rollers provided on an upstream side of the paper conveying path A0. These paired rollers 105 (first conveying unit, nip conveying unit) on the upstream side include a feed roller 105A and a reverse roller 105B. Reference numeral 106 denotes paired rollers (second conveying unit, nip conveying unit) provided on a downstream side of the paired rollers 105 on the upstream side. Reference numeral 107 denotes a pickup roller provided on the sheet accommodating unit 101 side. Of these rollers, each appropriate one is rotatingly driven at its location in an arrow direction to convey a paper. Between the paper feeding tray 109 and the external curved guide member 104, an intermediate guide member 108 is provided as an external guide that forms paper conveying path between these components 109 and 104.
However, in the paper conveying apparatus 102 configured as mentioned above, in the case of trying to convey a special paper with a relatively high stiffness or strength in a thickness direction of a subject to be conveyed, such as a paper S0 typified by a cardboard, or an envelop (hereinafter, “high-stiffness paper S0” or “high-strength paper S0”), since the radius of curvature of the curvature portion in the paper conveying path A0 is small, a resistance that occurs when the high-stiffness paper S0 is bent according to the curvature is significantly large compared with that of an ordinary paper for copy, for example. Therefore, there is a problem where it is difficult to smoothly advance the high-stiffness paper S0, causing a jam or faulty conveyance to make a stable feeding operation impossible.
The operation mentioned above is explained in further detail as follows. That is, in the paper conveying apparatus 102 in FIG. 16, the paper S0 is conveyed from the upstream paired rollers 105 provided in the paper conveying path A0, and when the tip of the paper S0 in a conveying direction reaches the curved guide member 103, the front-half of the paper S0 on the tip side is curved in a thickness direction by the fixed guide surface 103A of the curved guide member 103. Therefore, when the high-stiffness paper S0 is conveyed between the curved guide members 103 and 104, a resistance acted on this high-stiffness paper S0 against the curve is increased, thereby increasing a resistance against conveyance. Therefore, the tip side of the high-stiffness paper S0 does not reach the downstream paired rollers 106, and the high-stiffness paper S0 is conveyed only by the upstream paired rollers 105. When the high-stiffness paper S0 is bent by the curved guide member 103, only the conveying force by these upstream paired rollers 105 is not enough as an advancing force in a conveying direction against the resistance from the bent high-stiffness paper S0. For this reason, a faulty conveyance and a paper jam tend to occur. For example, a faulty conveyance may occur such that the center line of the high-stiffness paper S0 does not coincide with the center line of the conveying path. Also, for example, a paper jam may occur such that the high-stiffness paper S0 is caught in the curved guide member 103 and stops there.
On the other hand, in the paper conveying apparatus as mentioned above that is configured to change the paper conveying direction to a predetermined direction for conveyance, the rear end of the paper to be conveyed collides with a certain guide member in an impactive manner, depending on the shape of the guide member, in the course of conveyance in the paper conveying apparatus, thereby posing a problem of causing an unusual sound, such as a so-called clicking sound. In particular, in the case of conveying a paper with a high stiffness or strength in the thickness direction, that is, a high-stiffness paper, such as a cardboard, with a conveying force sufficiently larger than a conveying load being provided onto the paper, such an unusual sound as mentioned above tends to occur more significantly in the course of paper conveyance.
That is, firstly, as shown in FIG. 17, in the course of paper conveyance from the pickup roller 107 to the feed roller 105A, with a difference in height between the downstream end of the paper conveying direction on a paper stacking surface 101A and the guide member positioned on the downstream side of the paper conveying direction near the downstream end of the paper stacking surface 101A, a clicking sound occurs when the rear end of the paper goes across this difference. In more detail, a difference in height causes such a clicking sound as mentioned above when a guide surface 109A formed on the paper feeding tray 109 and positioned on the downstream side in the paper conveying direction near the paper stacking surface 101A defined by the paper S0 on top accommodated in the sheet accommodating unit 101 occupies a lower position relatively slightly away from the paper conveying path with reference thereto so as to form a predetermined space between these components 101A and 109A.
That is, in the course of paper conveyance, when the rear end of the paper S0 on top left on the paper feeding tray 109 moves from the paper stacking surface 101A to the guide surface 109A of the paper feeding tray 109, the rear end of the paper S0 collides with the guide surface 109A in an impactive manner, as depicted with a dotted line in the drawing. In particular, the high-stiffness paper S0 has a high flat-shape maintaining ability, and even if deformed, the ability of elastic returning to the flat shape is high. Therefore, this high ability of elastic returning to the flat shape promotes the tendency of the rear end of the paper S0 colliding with the guide surface in an impactive manner when moving as mentioned above, thereby making the clicking sound more significant. That is, the clicking sound occurring in the course of paper conveyance at the time of conveying a high-stiffness paper is larger than other sounds occurring in association with paper conveyance, and is significant as an unusual sound (impactive sound).
Also, as shown in FIG. 18, in the course of paper conveyance from the pickup roller 107 to the feed roller 105A, when a difference in height between the guide surface 109A of the paper feeding tray 109 and the external guide is present, a clicking sound occurs even when a rear end S0e of the paper S0 goes across the difference. That is, when an upstream end of the paper conveying direction on a guide surface 108A formed on intermediate guide member 108 as an external guide member on the downstream side of the paper conveying direction near the guide surface 109A of the paper feeding tray 109 occupies a lower position relatively slightly away from the paper conveying path with reference thereto, and forms predetermined space between these components 109A and 108A, the difference in height causes a clicking sound, as mentioned above. At the time of conveying a high-stiffness paper S0, a more significant clicking sound occurs, as mentioned with reference to FIG. 17.
Furthermore, as shown in FIG. 19, when a difference in height between the guide members forming an external guide is present between the feed roller 105A as a pre-turn roller and the paired rollers 106, a clicking sound also occurs when the rear end S0e of the paper S0 being conveyed goes over that difference. That is, among the guide members forming the paper conveying path A0, when an upstream end of the paper conveying direction on the curved guide member 104 occupies a lower position relatively slightly away from the paper conveying direction with reference thereto compared with a downstream end of the paper conveying direction on the guide surface 108A formed on the intermediate guide member 108 and a predetermined space is present between these components 108A and 104, the difference in height causes a clicking sound, as explained with reference to FIGS. 17 and 18. At the time of conveying the high-stiffness paper S0, a significant clicking sound occurs as mentioned above.
In summary, in some of the guide members forming a paper conveying path disposed on an outer-area side, consider a case where, compared with the downstream end of the paper conveying direction on a guide surface formed on one of guide members near the paper conveying direction, the upstream end of the paper conveying direction on a guide surface formed on the other following guide member is displaced in a direction of going a predetermined distance away from the paper conveying path. In this case, with the advancement of paper conveyance, when the rear end of the paper passes through one guide surface and then goes away from the downstream end of that guide surface, the rear end of the paper quickly moves in the going-away direction mentioned above to collide with the upstream end of the guide member, thereby causing an impactive clicking sound. Depending on the state of deformation in a thickness direction of the paper in the course of paper conveyance and the stiffness strength of the paper itself, the impact of the rear end of the paper is large, thereby causing a large volume of a clicking sound.
On the other hand, as shown in FIG. 20, between the feed roller 105A and the paired rollers 106, when the curved guide member 104, which is an external guide member, turns the paper S by, for example, bending the paper S as shown in states provided with reference characters Xb to Xd, that is, when the conveyed paper is in a state provided with a reference characters Xa in the case where the guide shape is such that a direction in which the tip of the paper S advances is turned to a predetermined direction by bending a portion on a rear end side of the paper S rather than the tip thereof, that is, when the tip of the paper S collides with the curved guide surface A0, the paper conveying load is larger than that of the states provided with other reference characters Xb to Xd. In particular, at the time of conveying a high-stiffness paper, the paper conveying load is larger than that of a normal-stiffness paper in any of the paper conveying states provided with the reference characters Xa to Xd. Similarly, when the tip of the high-stiffness paper S collides with the curved guide surface A0 (Xa), the load becomes the largest.
To get around this problem, in a paper feeding device disclosed in Japanese Patent Application Laid-Open No. 2004-338923, pp. 1-3, FIGS. 1-7 (hereinafter, “first patent document”) that conveys a sheet conveyed from the first conveying unit to a second conveying unit positioned approximately vertically above on a downstream side of a conveying direction, a pair of linear guide members are provided between the first conveying unit and the second conveying unit, and a sheet is conveyed with the guide of these linear guide members. According to this paper conveying device, the guide members are not in a curved shape but in a linear shape. Therefore, the conveying load can be reduced, that is, an abrupt change in load can be suppressed, thereby preventing a faulty conveyance, such as a paper jam or an oblique slip.
In short, according to the paper feeding device, without concentrating a deformed portion on the sheet to be conveyed on one portion bent by a curved guide member, the deformed portion can be distributed to two portions at front and rear ends of the linear guide members in the conveying direction. Furthermore, the linear guide members are diagonally placed at an approximately intermediate angle to make the degree of curvature at these portions approximately equal to each other, thereby suppressing an abrupt change in conveying load at the time of conveyance. That is, when a sheet advancing direction is changed, two portions are bent: a portion where the sheet is passed from upstream paired rollers to the linear guide members and a portion where the sheet is passed from the linear guide members to downstream paired rollers. This makes each of the degree of curvature at least small. With this, the resistance occurring by bending each portion can be kept low, thereby preventing an abrupt increase in conveying load.
Another paper feeding device has been known (for example, refer to Japanese Patent Application Laid-Open No. 2005-89008, pp. 2-3, FIGS. 4 and 5 (hereinafter, “second patent document”)). In this paper feeding device, first and second conveying units configured in a manner similar to those of the conventional paper conveying apparatus shown in FIG. 16 and the paper feeding device disclosed in Japanese Patent Application Laid-Open No. 2004-338923 (the first patent document), and a reverse guide member that forms an inclined surface leading to the second conveying unit is provided between the first and second conveying units. This reverse guide member is configured to be movable toward the second conveying unit.
According to the paper feeding device, when the rear end of a sheet makes contact with the reverse guide member, the reverse guide member is displaced in a direction in which the rear end of the sheet makes contact. With this displacement, a shock at the time of contact can be absorbed, thereby reducing a touch sound.
Also, a sheet feeding device has been known (for example, refer to Japanese Patent Application Laid-Open No. 10-129883, pp. 1-2, FIG. 1 (hereinafter, “third patent document”)). In this sheet feeding device, a plurality of sheet accommodating units that accommodate sheets are provided, each of which is individually provided with a conveying path and a sheet feeding unit, wherein an end of the conveying path is joined to one common conveying path. Also, at least a conveying path provided to a sheet accommodating unit that accommodates high-stiffness sheets has provided at its end a first curvature portion for joining to the common conveying path, the first curvature portion having a radius of curvature set larger than a radius of curvature of other curvature portions for joining provided to other conveying path.
According to the sheet feeding device, at the time of conveyance, when a high-stiffness sheet advances on the conveying path to pass through the first curvature portion with a large radius of curvature, the high-stiffness sheet is prevented from being bent to a degree similar to that for an ordinary sheet, and continues to advance as being sufficiently mildly bent. With this, the resistance at the time of conveyance can be small, thereby causing the high-stiffness sheet to reach the common conveying path for conveyance without a sheet jam or delay.
Furthermore, a sheet reversing unit provided to an image forming apparatus has been known (for example, refer to Japanese Patent Application Laid-Open No. 2005-1771, pp. 1-2, FIG. 1 (hereinafter, “fourth patent document”)). In this sheet reversing unit, paired reverse rollers and a reverse conveying path for conveying and guiding a sheet fed from these paired reverse rollers are provided. The reverse conveying path has a direction-change portion for changing a sheet conveying direction. A rotatable roller is disposed inside the direction-change portion in a right-angle direction when viewed in the sheet conveying direction. With this, the sheet fed to the reverse conveying path is sent in contact with the rollers.
According to the sheet reversing unit, an inner contact portion of the fed sheet always makes contact at the direction-change portion with the rollers. Also, these rollers are driven in association with advancement of the sheet in the conveying direction. Therefore, compared with a conventional guide plate, the conveying resistance can be small. That is, a friction resistance occurring between the fixed guide member and the moving sheet is resolved, thereby achieving a guide that changes a conveying direction at the direction-change portion.
However, in the conventional paper conveying apparatus and the sheet conveying apparatus disclosed in the first patent document shown in FIGS. 16 to 20, the configuration is such that a fixed member for guiding a sheet to be conveyed is merely disposed, after all. Therefore, a difference in speed between the moving sheet to be conveyed and the fixed guide member cannot be resolved. This poses a problem where a resistance acting in a direction hindering the sheet conveyance always occurs irrespectively of the shape or installation position of the guide member, and serves as a conveying load.
That is, in the conventional configuration, the effects of preventing the jam and faulty conveyance mentioned above are insufficient. Even though the linear guide members can suppress an abrupt increase in conveying load, the occurrence of the conveying load cannot be eliminated. In particular, when a high-stiffness paper (sheet), such as a cardboard or an envelope, is to be conveyed, the fault conveyance and jam mentioned above and a clicking sound of the rear end of the paper are significant.
In the configuration disclosed in the second patent document in which a reverse guide member is provided, even if the reverse guide member is a movable member in a sense of capable of being displaced in a direction in which the rear end of the paper makes contact, the reverse guide member is a fixed guide member as a guide for changing the orientation of the paper. Similarly, when guiding with the orientation being changed, a relative difference between the paper and the reverse guide member is not resolved, thereby causing a conveying load. In particular, when a high-stiffness paper (sheet), such as a cardboard or an envelope, is to be conveyed, the fault conveyance and jam mentioned above and a clicking sound of the rear end of the paper are significant.
Furthermore, even in the configuration as disclosed in the third patent document in which a dedicated conveying path with its radius of curvature being set at a predetermined large value, the sheet advancing on this dedicated conveying path is mildly bent, thereby reducing a conveying load of the sheet receiving from the conveyor path, but the occurrence of the conveying load cannot be eliminated similarly to the above. In particular, when a high-stiffness paper (sheet), such as a cardboard or an envelope, is to be conveyed, the fault conveyance and jam mentioned above are significant.
Still further, in the configuration disclosed in the fourth patent document in which movable members, such as rollers, are provided at predetermined positions on the inner conveying path portion at the direction-change portion of the conveying path, in the course of conveyance, even if the inner rollers can particularly effectively reduce a friction resistance between the front and rear ends of the sheet with an intermediate portion being supported, no consideration is given to a conveying load before and after the state explained above, that is, a conveying load when the external conveying path portion at the direction-change portion and the sheet make contact with each other. Also, no particular mention is made of behaviors of the tip and rear end of the sheet in the course of conveyance. In particular, when a high-stiffness paper (sheet), such as a cardboard or an envelope, is to be conveyed, the fault conveyance and jam mentioned above and a clicking sound of the rear end of the paper are significant.